This invention relates to a system for continuously lubricating critical areas on a shaft including bushings and seals. Most preferably, the invention is used on a cam brake shaft.
Typically, a cam brake shaft comprises an inside end that is driven to rotate in response to braking input by a vehicle operator, an outer cam end that rotates and forces outward movement of brake pads into a respective wheel. The shaft rotates within a tubular cam shaft housing. The tubular cam shaft housing is lined in part with a plurality of bushings and has at least one seal positioned at either end.
The design of cam brake shaft systems presents many challenges. One such challenge occurs with respect to keeping the cam shaft properly lubricated, and particularly in the bushing and seal areas of the cam housing. Over time, grease or other lubricant tends to escape the bearing areas. This has often required periodic refreshing of the lubricant. Lack of consistent lubrication at these critical areas can lead to malfunctioning components or even seizure. A well lubricated cam brake shaft ultimately results in a longer life for the cam brake shaft elements.
It would be desirable to provide a cam brake shaft with a system for continuously supplying a fresh source of lubrication to the critical bushing and seal areas of the cam brake shaft.
In the disclosed embodiment of this invention, a cam brake shaft is provided with a system for continuously supplying a fresh source of lubrication to the critical bushing and seal areas of the cam brake shaft at a generally constant pressure. This is accomplished using a centrally located bias element, such as a spring, and an adjacent pair of axially sliding inboard seals. The biased inboard seals apply a continuous pressure to lubricating fluid between a pair of main seals at each end of the tubular cam housing and respective ones of the inboard seals positioned at ends of the centrally located spring.
An elongate portion of the cam brake shaft that lies between the inner and outer ends rotates within a hollow tubular cam housing. A main seal is provided within each of the two housing ends. Next to each main seal, axially inward of the cam housing is each of a pair of laterally spaced bushings. The bushings guide the elongate portion of the cam shaft.
In the interior of the cam housing there is a tubular shaped space surrounding the elongate portion of the cam shaft between the laterally spaced bushings. The bias spring is coiled about a midsection of the elongate portion of the cam shaft within the tubular shaped space. The spring has two ends, each of which abuts the axially sliding inboard seals. Thus the tubular shaped space is generally segmented into three portions. There is the central portion which houses the spring and abutting inboard seals, and two laterally spaced outward tubular shaped areas. Each outward tubular shaped area is positioned between each sliding inboard seal and its respective bushing.
Lubricating fluid is introduced to the cam shaft housing by way of a pair of inlet fittings, each positioned in the area of the laterally spaced outward tubular shaped areas. Thus, lubricating fluid enters each outwardly spaced tubular shaped area, and exerts a compressive force on the spring through the sliding inboard seals.
As the spring resists the compressive force, it exerts an opposing force on each of the two sliding inboard seals. This, in turn, forces the lubricating fluid in opposing directions towards each laterally spaced bushing where it lubricates the inner bushing surfaces as the cam shaft rotates. Over time, as the vehicle brake is applied and released and as lubricating fluid seeps out past the laterally spaced main seals, fresh lubricating fluid is forced between cam shaft and bushing surfaces and against the main seals. An air purge may need to take place initially. Air purge devices may be located at an opening in the cam housing positioned in the area of each bushing.
These and other features of the present invention can be best understood from the following specification and drawing, the following of which is a brief description.